1. Field of the Invention
The present invention relates to a device for controlling an engine including an ISC (idle speed control) device for controlling the idle speed of the engine and also relates to a method of controlling such engine.
2. Description of the Related Art
As a conventional engine, there is known an engine including an ISC device that controls the idle speed to be at a target speed by having an upper side and a lower side of a throttle valve installed in an intake passage connected by an intake bypass passage. The ISC device includes an ISC valve disposed in the intake bypass passage so as to adjust the amount of air flowing through the intake bypass passage by the ISC valve at the time of idling.
With a vehicle on which an engine including such an ISC device is mounted, an ISC valve of the ISC device may become fixed (adheres) at an open state due to a short circuiting of wirings, carbon deposit or the like on the ISC valve. In a state where the ISC valve is fixed, the amount of intake air into the engine increases compared to a normal state (non-fixed state), and thus, the idle speed of the engine increases. As a result, there is a possibility that an automatic centrifugal clutch is connected even if the throttle valve is completely closed, and that the vehicle is unintentionally started.
Accordingly, as described, for example, in Patent Document 1 (Japanese Patent Laid-Open Publication No. 60-11648), a technique is proposed of calculating in advance the basic amount of air that is based on the degree of opening of a throttle valve and the engine speed, and determining an abnormality in an ISC valve when a measurement value of the amount of actually measured engine air intake exceeds the basic amount of air.
Furthermore, as described in Patent Document 2 (Japanese Patent Laid-Open Publication No. 8-86266), there is provided a technique of calculating the actual amount of intake air flowing through an ISC valve by calculating the amount of intake air flowing through a throttle valve based on the degree of opening of the throttle valve and deducting the amount of intake air flowing through the throttle valve from the amount of intake air (a measurement value) of the entire mechanism, and determining an abnormality in the ISC valve in a case where there is a predetermined or greater deviation between the actual amount of intake air and the amount of intake air calculated based on a set degree of opening of the ISC valve.
The conventional techniques described in Patent Documents 1 and 2 are suitable when applied to a so-called L-jetronic fuel injection device that detects the amount of intake air into the engine by an air flow sensor, but are not suitable for a D-jetronic fuel injection device that detects an intake air pressure (an intake negative pressure) and decides the amount of fuel injection, because an air flow sensor has to be separately provided.
Generally, the D-jetronic fuel injection device is said to be more advantageous compared to the L-jetronic fuel injection device in a viewpoint such that, since the air flow sensor is unnecessary, an increase in the intake resistance can be prevented.
Furthermore, in contrast to the L-jetronic fuel injection device that decides the optimal amount of fuel injection after measuring the actual amount of intake air, the D-jetronic fuel injection device decides the amount of fuel injection by measuring a change in the intake negative pressure that causes a change in the amount of intake air, and thus, it is also advantageous in that it has good responsiveness for the output change with respect to a throttle operation.
For these reasons, the D-jetronic fuel injection device is widely used in motorcycles and all terrain vehicles and, accordingly, it is difficult to apply the conventional technique described in Patent Document 1 or 2 to motorcycles and all terrain vehicles.